Ensure crypto instructions are used on AAarch32 & AAarch64 when available.

[briansmith]

Grep for BORINGSSL_CLANG_SUPPORTS_DOT_ARCH. We need to ensure that that code is enabled in all AAarch32 and AAarch64 builds that use dynamic feature detection. Note that the Perl code seems to say that it is 64-bit only. I'm not sure if that's intended.

[briansmith]

See https://llvm.org/bugs/show_bug.cgi?id=26016 and https://bugs.chromium.org/p/boringssl/issues/detail?id=39.

[briansmith]

See also https://boringssl-review.googlesource.com/c/4411/1/crypto/aes/asm/aesv8-armx.pl#43, in particular the way that PerlAsm sometimes treats .arch as a no-op.

[briansmith]

Depends on the refactoring in #408, at least.

[pietro]

After #473 I think we can always define BORINGSSL_CLANG_SUPPORTS_DOT_ARCH on android.

[valpackett]

I recently landed FreeBSD/aarch64 support in stdsimd (by using the mrs instruction in userspace) rust-lang/stdarch#611 — that method is also supported on Linux since 4.11.